Picture-transmitting system



May 22, 1928.

H. NYQUIST PICTURE TRANSMITTING SYSTEM Fi led Dec. 17, 1924 ghets-sheet l INVENTOR E JV ATTORNEY May 22, 1928.

Filed Dec. 17, 1924 2 Sheets-Sheet 2 I l l l |L I I II II II 1 a Q W w t 0 Q G 0 7 mist BY ATTORNEY Patented May 22, 1928.

UNITED STATES PATENT orrica.

HARDY GUM, OI MU, NEW JERSEY, ASSIGHOB 'I'O AMERICAN rumor! v AID TELEGRAPH 001mm, A. CORPORATION 01 NEW You.

IPIC'I'UBE-MBII'ISTING BYBTEI.

Application ma December 11, 1924. w No. 150,509.

An object of my invention is to provide a new and improved system for transmitting pictures electrically. Another object of'my invention is to provide for record ng a received icture in such a system in halftone ots. Another object of my invention is to send a picture on a carrier current and to utilize the carrier current half-waves to record respective half-tone dots in the received icture. These and various other objects my invention will become apparent on consideration of an example w 1ch I have chosen for disclosure in the following s ecification taken with the accom anymg rawings. it will be understood t at the description which follows relates to this example of the invention and that the invention will be defined in the appended claims.

Referrin' to the drawings, Figure 1 is a diagram 0 a transmitting station embodying my invention; Fig. 2 is a diagram of a corresponding receiving station; and Fig. 3 is a diagram illustratin the production of the half-tone record at t e receiving station.

The cylindrical drum 28 at the transmittin station has the picture wrapped about it in the form of a semi-transparent film. This drum 28 is mounted on the axial screwthreaded shaft 27 in engagement with the screw-threaded support 24, so that as the drum 28 rotates it is traversed slowly in the direction of its axis. It is driven by the motor 21 through the sliding connection 26.

The same motor 21 drives two generators 22 and 23. The generator 22 produces a low frequency current which goes through the low pass filter 36 to the line 37. The generator 23 produces a high frequency current which goes to the modulator 34.

The light from the source 31 is focused by the lens on an opening in the screen 29 adjacent to the film on the drum 28. Ach cordin ly the quantity of light falling on the pli otdelectric cell 32 will be varied in correspondence with the degree of shade in the spot of the film underlying the opening in the screen 29.

In accordance with the principle of the photoelectric cell, the current therefrom will vary in accordance with the quantity of light fall' g on it and this current goes to the input of the amplifier 33 whose output oes to modulate the carrier current applie to the modulator 34. This modulated output then goes from 34, filter 35 to the line 37.

At the receiving station the incoming cur.- rents on the line 37 go through the amplifier 38 and thence to respective branch circuits as determined b the two filters in parallel, one of them t e high as's filter 39 and the other the low pass fi ter 40. The low frequency current from the low pass filter 40 goes through the amplifier 42 and drives the synchronous motor 51. This current is the current whose frequency is determined by the generator 22 at the sending station.

The high frequency current from the high pass filter 39 goes through the amplifier 41 to the light valve 43.

Through the sliding connection 49, the receiving drum 46 is rotated by the synchronous motor 51 in synchronlsm with the drum 28 at the sending end. The axial shaft 47 carrying the drum 46 has screwthreaded'engagement with the support 48 so that the drum 46 traversed in synchronism with the drum 28 at the sending end.

, Light from the source 45 is focused by the lens 44 on the light valve 43. This light valve consists of a shutter (see Fig. 3) which normally stands across an opening 61 as indicated at 60. This shutter 60 is deflected to one side or the other by the magnetic action of the current to the light valve. When this current is an alternating carrier current of varying amplitude, then the light valve vibrates, opening first one side and then the other of the orifice 61, and for small amplitudes these side 0 enings will be slight but for large amplitudgs they will be great, the maximum opening being the entire width of the orifice 61.

Suppose that the picture to be transmitted as an area of intermediate shade passing under the opening in the screen 29 at the sending end, so that the current to the light valve 43 in Fig. 2 is of intermediate amplitude; then the shutter 60 will vibrate rom the extreme position shown at the top of Fig. 3 through the position indicated at 60' to that indicated at 60 and back, and so not only rotates but is.

through the high m.

on. When the shutter is at the position 60 in Fig. 3, the sensitive film represented in the lower art of F i 3 has the line H directly un er the lig t valve opening 61, as indicated by the line a-a', and the exposed portion of the film is 62 for the opening of the right-hand end of the orifice 61. When the shutter returns to the median position shown at 60, the film has moved on so that the line 6-5 is directl under the closed orifice 61 as indicated by b--b'. Then the shutter swings to the right as shown at 60" and for the corresponding opening of the orifice 61, the record on the film is shown at 62'.

In this way the series of staggered halfdots are recorded along the range 63 which represents a single linear helical element of the receiving film passing under the or1- fice 61.

The next adjacent linear helical element of the receiving film is designated (53 in Fig. 3 and this passes next under the orifice 61, and assuming that the picture shade continues the same, another series of staggered half-dots is made as shown within the brace 63' on Fig. 3.

The synchronism is established so that the half-dots at the left in the range 63 register with the half-dots at the right in the range 63, making complete dots as, for example, at 67. The ranges comprehended by the brace numbered 66 all correspond to an intermediate picture shade. The ranges within the brace 64 correspond to a light picture shade in the receiving film; here the amplitude of the vibration of the shutter 60 is very slight, corresponding to a small amplitude for the carrier current. On the other hand, within the ranges embraced by the numeral 65 the amplitude of the vibration of the shutter is a maximum, corresponding to a dark shade in the receiving film.

It will be noticed that the half-tone dots in Fig. 3 lie most closely together along diagonal lines at 45 degrees to the vertical or horizontal, which is desirable in half-tone pictures. In accordance with the present invention, the received film is a half-tone film ready for use in the half-tone printing process, not requiring the use of a ruled screen or other such expedient to get half-tone dots.

It will be seen that the system must be devised and adjusted so that the synchronizing current shall have a definite constant frequency relation to the carrier current. This is secured by operating the generators of the two currents from the same motor 21 as in Fig. 1 and also driving the sending drum 28 from the same motor and driving the receiving drum from a synchronous motor.

I claim:

1.. The method of transmitting a picture,

which consists in modulating a carrier current according to the degree of shade of successive picture elements, applying the modulated carrier current to o erate a light valve, and passing a sensitive fi m under said light valve at a speed such that the successive operations of said valve corresponding to successive half-waves of carrier current will be recorded as separate half-tone areas.

2. The method of transmitting a picture,

which consists in modulating a carrier cnrrent according to the degree of shade of successive picture elements, applying the modulated carrier current to operate a light valve, and passing a sensitive film under said light valve at a speed such that the successive openings of said valve corresponding to successive half-waves of carrier current will produce dot records of magnitude corresponding to the amplitude of the carrier current.

3. The method of transmitting a picture, which consists in sending current impulses corresponding to the degree of shade of successive picture elements, appl ing these current impulses to operate a lig it valve, alternately and successively opening the two opposite ends of the li ht valve orifice, and moving a sensitive film at a definite rate with respect to the rate of operation of said light valve to produce on said film discrete half-tone dots correspondin to successive sending current impulses [Hit in area corresponding to the magnitude of the respective current impulses.

4. The method of transmitting a picture, which consists in modulating a carrier current according to the degree of shade of successive picture elements, applying the modulated carrier current to operate a light valve, alternately and successively opening the two opposite ends of the light valve orifice, and passing a sensitive film under said light valve in successive adjacent linear ranges, so that staggered half-dots are recorded on the film in each range and the half-dots of each range register with the half-dots of the adjacent ran es.

5. In combination, means to generate a carrier current, means to modulate it according to the degree of shade of successive elements of a picture to be transmitted, a light valve to which the modulated current is applied, a sensitive film, and means to move said film past said light valve at a speed sc related to the carrier current frequency that the distance moved per half-cycle shall bt of the same order as the maximum amplitude in the light valve.

6. In combination, means to generate i carrier current, means to modulate it accord ing to the degree of shade of successive ele ments in helical order of a picture wrapper on a cylindrical drum, a line to carry sucl modulated current, means to generate a syn chronous current definitely related to th movement of the said drum and put it lllSl on said line, means to move a cylindrical re ceiving film in helical order and in synchro nism determined by the s nchronizin current received from said inc, and 1 ing film. 5 7. In comblnation, in rent impulses correspo cans to generate curnding to the degree of shade of successive elements of a picture, means to apply said currents to operate a light valve, alternately 10 opening the two oppos and successively ite ends of the light valve orifice, and means to move a sensitive film under said light valve at such a s that its openings will record discrete half tone dots corresponding to the said current impulses to make the received picture.

In testimony whereof, I have signed m name to this specification this 15th day of December 1924.

HARRY NYQUIST. 

